1. Field of the Invention
Embodiments of the present invention relate to a liquid crystal display device, and more particularly, to a backlight apparatus for a liquid crystal display device. Embodiments of the present invention are suitable for a wide scope of applications. In particular, embodiments of the present invention are suitable for driving a backlight apparatus for a liquid crystal display device.
2. Discussion of Related Art
Recently, the liquid crystal display (LCD) devices have been widely used in portable videos, cameras, TV, computer monitors, mobile phones, vehicle navigation devices, and so on. The LCD device is a light-receiving display device that displays an image on an LCD panel by controlling the amount of externally provided input light. Thus, the LCD device requires a backlight unit for irradiating light onto the liquid crystal display panel.
The backlight unit uses a lamp as a light source and converts light from the lamp into a surface light having the same luminance and irradiates the converted light onto the LCD panel. The backlight unit can be classified into a direct type and an edge type depending on the location of the lamp. In the direct type backlight unit, the lamp is at the rear of the LCD panel, and light is directly transmitted to the front of the LCD panel. In contrast, in the edge type backlight unit, the lamp is disposed to the side of the LCD panel, and light is reflected, diffused and condensed through a wave-guide plate, a reflection sheet and an optical sheet, to be transmitted from the side to the front of the LCD panel.
The lamp may be a cold cathode fluorescent lamp (CCFL), an external electrode fluorescent lamp (EEFL), and a light-emitting diode (LED), etc. The backlight unit must apply a driving voltage to the lamp to emit light. The driving voltage is applied by a driver (or an inverter) provided in the backlight unit.
FIG. 1 is a block diagram of a backlight driving apparatus for an LCD device according to the related art. Referring to FIG. 1, the related art backlight driving apparatus has a light source 1 that emits light, and a backlight (B/L) driver 2 for controlling the lighting of the light source 1. The backlight driver 2 converts an externally provided DC input voltage into an AC voltage, boosts the AC voltage to a predetermined level, and supplies the boosted AC voltage to the light source 1. The backlight driver 2 supplies a sufficiently high voltage to turn on the light source 1 and controls the current of the light source 1 after the light source 1 has been turned on to maintain a constant luminance, in accordance with the characteristic of the light source 1.
For example, the physical properties of the LCD device might change due to a variation in the ambient environment, or the backlight unit might be changed, or the input voltage might fluctuate due to the instability of the input power. Then, the backlight driver 2 controls the current to provide a constant power to the light source 1. In particular, when the input voltage is low, the consumed current is high, and when the input voltage is high, the consumed current is low. However, if the input voltage is low and a high current is consumed, an excessive load is applied to the external power supply unit and the backlight driver 2 due to the excess current. Accordingly, the internal circuit of the backlight could be damaged causing the operation of backlight driver 2 to be unstable.